1. Field of the Invention.
The present invention relates to heat exchangers, and more particularly to heat exchanger support structures made substantially of fiber reinforced resin structural components.
2. Description of the Prior Art.
Prior heat exchangers have included cooling towers and evaporative condensers, for example. Cooling towers are used to cool liquid by contact with air. Many cooling towers are of the counterflow type, in which a warm liquid is allowed to flow downwardly through the tower while a counter current of air is drawn or pushed upwardly through the falling liquid to cool the liquid. Other cooling towers are of the cross-flow type, in which a cross-current of air is drawn or pushed across the falling liquid to cool the liquid. A common application for liquid cooling towers is for cooling water to dissipate waste heat in electrical generating and process plants and industrial and institutional air-conditioning systems.
Most cooling towers include a structural assembly to support dead and live loads, including air moving equipment such as a fan, motor, gearbox, drive shaft or coupling, liquid distribution equipment such as distribution headers and spray nozzles and heat transfer surface media such as fill media. The fill media generally has spaces through which the liquid flows downwardly and the air flows upwardly to provide heat and mass transfer between the liquid and the air. Structural parts of a cooling tower must not only support the weight of the fill material but must also resist wind forces or loads and should be designed to withstand earthquake loads.
Due to the corrosive nature of the great volumes of air and water drawn through such cooling towers, it has been the past practice to either assemble such cooling tower support structures of stainless steel or galvanized and coated metal, or for larger field assembled towers, to construct such cooling tower frames of wood, which is chemically treated under pressure, or concrete at least for the structural parts of the tower.
To withstand expected lateral wind and seismic loads, cooling tower support structures have generally been of two types: shear wall frame structures and laterally-braced frame structures. Shear wall frame structures are generally of fiber reinforced resin or concrete construction, and have a network of interconnected columns and beams, together with shear walls that provide lateral resistance to wind and earthquake loads. In concrete shear wall cooling towers, the joint connections between the columns and beams can be rigid if cast-in-place construction techniques are used. In concrete precast construction and in shear wall towers made of fiber reinforced resin columns and beams, the joints between the columns and beams are designed to allow for rotation between the columns and beams. In laterally braced framing structures, the cooling towers are generally made of wood or fiber reinforced resin beams and columns, framed conventionally for dead load support; and with diagonal braces to resist lateral loads, the frame being covered by a cladding material. The joints where the beams and columns meet are designed to allow for rotation between the structural elements. The joints do not provide lateral resistance to loading or racking of the structure.
Support structures made of concrete are very durable, but concrete cooling tower support structures are expensive and heavy. Many cooling towers are installed on the roofs of buildings, and the weight of a concrete cooling tower can present building design problems. In towers with metal support structures, corrosion of critical structural elements can be problematic in the wet environment. In towers with wood support structures, the wood may decay under the constant exposure to the wet environment. Wood that has been chemically treated to increase its useful life may have environmental disadvantages: the chemical treatment may leach from the wood into the water being cooled. Fiber reinforced resin material has been used successfully as a design alternative to concrete, metal and wood.
Prior art cooling towers using fiber reinforced resin structural elements include those shown in U.S. Pat. No. 5,236,625 to Bardo et al. (1993) and U.S. Pat. No. 5,028,357 (1991) to Bardo. Both patents disclose structures suitable for cooling towers. Another cooling tower using fiber reinforced resin structural components is disclosed in U.S. Pat. No. 5,851,446 to Bardo et al. (1998). In this cooling tower, fiber reinforced resin beams and columns are used along with mounting members. The columns and beams are bonded to the mounting members, and mechanical fasteners are also used to connect the mounting members to the columns and beams. The bonded joints do not allow for rotation between the columns and beams. After the frame of fiber reinforced resin columns and beams is built, a skin or cladding layer is attached in a separate step; the cladding is not intended to add significantly to the structural strength of the frame. Although in all of U.S. Pat. No. 5,236,625, U.S. Pat. No. 5,028,357 and U.S. Pat. No. 5,851,446, the cooling towers provide strong and efficiently-built structures, it is desirable to further reduce costs, particularly for smaller sized cooling towers.
In all of the cooling towers disclosed in U.S. Pat. No. 5,236,625, U.S. Pat. No. 5,028,357 and U.S. Pat. No. 5,851,446, the basins for collecting the cooled fluid that has passed through the fill material have generally flat surfaces, and the bottoms of the columns of the cooling towers are generally fixed to the flat surface of the basin. Typical basins for these cooling towers have been made of concrete or of flat thin pieces of fiber reinforced resin material supported by a steel grill structure. In some countries, such as in Australia and England, the basin structures are required by law to have sloping rather than flat surfaces. In U.S. Pat. No. 4,442,983, a cooling tower is disclosed with a basin made of fiber reinforced resin with sloping floors leading to a trough for collecting the cooled liquid. The entire basin is molded in a traditional manner. Such traditional molding can be expensive, and shipping of such a bulky structure further adds to the expense.
Other heat exchangers, such as evaporative condensers, have used similar support structures. However, instead of fill material within the structure, the condensers use coils of tubes within which a process fluid is condensed. Some condensers utilize evaporative heat exchange, with an evaporative liquid distributed over the condenser coils and collected in a basin below. Problems with the support structures and basin structures generally parallel those described above for cooling towers.